The hypothesis on which these studies are based is that certain noncollagenous proteins (NCPs) are involved in the controlled deposition of apatite crystals onto the collagen matrix in dentin. The first approach to testing this hypothesis is to completely assess the nature of all the NCPs in rat dentin. Consequently careful extraction and preparative procedures were utilized to eliminate enzymatic degradation and losses of proteins. The macromolecules obtained from rat incisor dentin fell into four categories: (1) proteoglycans (2) acidic glycoproteins (3) gamma-carbosyglutamic acid (Gla)-containing proteins and (4) phosphoproteins. The physical and chemical properties of these substances are being studied. In order to determine the biological role played by these substances, we have developed an odontoblast organ culture system. Studies are being conducted to characterize the potential of this system for duplicating in vivo events of dentinogenesis. Later studies with the odontoblast cultures will involve the assessment of the metabolic interrelations (if any) of the NCPs of rat dentin.